1. Field of the Invention
This invention relates to heat and flame resistant, flexible, insulating fabric compositions. More particularly, it relates to refractory coated and dielectric coated base fabric compositions. This invention especially relates to refractory coated and dielectric coated base fabric compositions wherein the refractory coating is formed on one side of the fabric and the dielectric coating is formed on the other side.
2. Description of the Prior Art
Asbestos and other thermal protection materials are employed as protective mats for welding operations, furnace linings, fire-resistant linings and the like to provide protection from flames and thermal extremes as well as for dissipation of heat at a high rate. Although in each application reasonable performance is obtained, the selected material has limitations in its range of uses and in its effectiveness, even in uses for which it is particularly adapted. In addition, asbestos has found less utility in certain uses because of recent findings that it may constitute a health hazard.
Ceramics and/or glass fibers have been used heretofore to prepare high temperature electrical insulating tape. In addition, coated fabrics and ceramic structures have been prepared with a combination of glass fiber fabrics and metal oxides.
U.S. Pat. No. 4,282,284 and commonly assigned patent applications Ser. Nos. 225,888 and 294,770 disclose a heat resistant, flexible, refractory, insulating fabric composition of a porous base fabric, preferably a knitted fiberglass fabric, coated with heat resistant refractory materials, such as alumina and zirconia, and an organic bonding agent, such as acrylic latex alone or admixed with colloidal silica. A polymeric coating, such as polyvinyl chloride, may be formed over the coated fabric to provide abrasion resistance to the composition. A feature of this composition resides in the fact that the refractory materials are bonded in the interstices as well as to the surface of the base fabric, such that a significant amount of the fabric's flexibility and stretch properties are retained. This fabric composition has a variety of uses and therefore may be employed as the dielectric in insulated electrical wire or cable, as protective mats and curtains in welding operations, as linings for fire resistant machine and appliance covers, as duct and pipe insulation, as wrappings for engine exhaust systems and the like. When this fabric composition is exposed to heat and high temperatures, the organic bonding agent containing the refractory materials will decompose, causing the refractory materials to fuse into the softened surface of the knit fiberglass base fabric, enabling it to withstand intense heat and elevated temperatures well beyond the normal melt temperature of the fiberglass fabric. The resulting fabric structure will have ceramic qualities and will not soften, melt, drip or lose its insulating properties.
Although the organic components of the bonding agent of these prior art fabric compositions may not produce a flame when exposed to a flame or the intense heat developed by a flame, i.e. temperature of 1750.degree. F. and above, they will decompose at these temperatures resulting in some products of combustion in the form of smoke and fumes which may prove harmful to persons in the vicinity.
Commonly assigned patent application Ser. No. 294,771 discloses improved refractory coated fabric compositions which eliminate the products of combustion which may be formed with the fabric compositions described above. These improved fabric compositions are similar to those which produce products of combustion in all respects except that an inorganic bonding agent is substituted for the organic bonding agent of the prior art fabric compositions. When these fabric compositions with the inorganic bonding agent are exposed to high temperatures above about 1750.degree. F., no products of combustion in the form of smoke or fumes are produced.
Another commonly assigned patent application, filed concurrently herewith, discloses the use of plasma spraying to form refractory coatings on base fabric. These coated fabric compositions differ from those disclosed in the above patent and patent applications in that plasma sprayed refractory coatings contain no added bonding agent. Further, the plasma spraying method permits the preparation of thinner refractory coatings than those of the prior art compositions.
The refractory coated fabric compositions disclosed in the commonly assigned patent and patent applications may be usefully employed as insulating tape for electrical conductors. Although these fabric compositions exhibit good dielectric properties, the state of the art requires flame resistant, electrical insulating compositions having dielectric properties superior to those presently available.
It is an object of this invention to provide refractory coated fabric compositions having improved dielectric properties.
It is another object of this invention to provide compositions which may be usefully employed in insulating electrical conductors and which will exhibit superior dielectric properties as well as superior flame and heat resistance properties.
It is a further object of this invention to provide a dual function fabric composition having superior dielectric and superior flame and heat resistance properties.